1. Field of the Invention
The present invention relates to a light-emitting diode (hereinafter also referred to as “LED”) lamp capable of preventing failure in electrical connection between a light-emitting element and a metal pattern of an electrically conducting portion. Particularly, it relates to an LED lamp using a resin frame member such as a lamp house.
Incidentally, in this specification, an LED chip per se is referred to as “light-emitting element”. An LED chip packed in a package resin or an LED chip including an optical device such as a lens system is collectively referred to as “light-emitting diode lamp” or “LED lamp”.
2. Description of the Related Art
[Patent Document 1] JP-A-8-330637
A surface-mounting type light-emitting diode according to the related art has the following disadvantages. Because a metal pattern (electrically conducting portion) on a substrate is nipped by a seal mold when a resin sealing portion is formed, there is a possibility that the metal pattern may crack. There is also a possibility that the metal pattern and the resin sealing portion may be separated from each other because of a difference in thermal expansion coefficient between the metal pattern and the resin sealing portion in a high temperature process in a solder reflow furnace or the like. Therefore, in an invention disclosed in Patent Document 1, a resist is put between the metal pattern on the substrate and the resin sealing portion. The resist is flexible and acts as a cushioning medium. Accordingly, the flexible resist is deformed to absorb pressure of the seal mold to thereby prevent the metal pattern from cracking. In addition, stress caused by the difference in thermal expansion coefficient between the metal pattern and the resin sealing portion in the high temperature process is absorbed to the resist to thereby prevent the metal pattern and the resin sealing portion from being separated from each other.
A surface of the metal pattern is generally plated with gold because gold is excellent in solder wettability and corrosion protection. The gold-plated surface is however poor in adhesion because it is not rough but smooth. For this reason, even in accordance with the invention disclosed in Patent Document 1, there is a possibility that the separation cannot be prevented sufficiently. Such a case will be described with reference to FIGS. 5A and 5B. FIG. 5A is a vertical sectional view showing a vertical section of an end portion of a related-art LED lamp having a lamp house provided in the periphery of a light-emitting element. FIG. 5B is a vertical sectional view showing a vertical section of an end portion of a related-art LED lamp having a resist layer provided between a lamp house and a metal pattern. Incidentally, the light-emitting element is not shown in each of FIGS. 5A and 5B but is mounted in a central portion of the LED lamp on the left side of each of FIGS. 5A and 5B.
As shown in FIG. 5A, in the LED lamp 20, a metal pattern composed of three layers of copper 14, nickel 15 and gold 16 is formed on a glass epoxy substrate 2 by plating. The reason why the metal pattern is composed of three layers is as follows. Copper 14 is good in adhesion to the glass epoxy substrate 2. Gold 16 is good in solder wettability and excellent in corrosion protection as described above. It is therefore preferable that gold 16 is provided as an outer surface of the metal pattern. Adhesion between copper 14 and gold 16 is however poor. Therefore, nickel 15 excellent in adhesion both to copper 14 and to gold 16 is put between copper 14 and gold 16.
A lamp house 8 made of a white resin is bonded onto the metal pattern by an adhesive agent 7. The lamp house 8 has a taper surface 8a which will serve as a reflecting mirror when the taper surface 8a encircles the light-emitting element. The light-emitting element not shown is then mounted on the surface (gold) 16 of the metal pattern in the central portion of the lamp house 8. After the light-emitting element and the metal pattern are electrically connected to each other by wire bonding, a transparent epoxy resin 9 is packed in the frame of the lamp house 8 and hardened by heating. As a result, the light-emitting element is sealed with the resin. In this manner, the LED lamp 20 is produced.
If the LED lamp 20 is then exposed to a high temperature process in a solder dip or reflow furnace or the like, the metal pattern (14, 15, 16) and the resin portion (7, 8, 9) are however separated from each other because of stress caused by a difference in thermal expansion coefficient between the metal pattern and the resin portion. If the separation comes to the central portion of the LED lamp 20, a product defective in electrical connection/lighting is produced because wires of the light-emitting element sealed with the transparent epoxy resin 9 are separated from the surface (gold) 16 of the metal pattern. Therefore, as shown in FIG. 5B, it may be conceived that a resist 3 is put between the metal pattern and the resin portion in the same manner as in the technique described in Patent Document 1 so that the resist 3 serves as a cushioning medium. Also in this case, the problem in separation caused by thermal stress still remains unsolved because the surface of the metal pattern is made of gold 16 smooth but poor in adhesion and because the resist 3 is made of an epoxy resin.